标题： 星系对其最近的星团了解多少 显示英文标题

标题： What galaxies know about their nearest cluster

摘要： 我们研究了星系的恒星形成历史和形态在多大程度上由它们到星团中心的距离以及最近星团的丰富度决定。 我们观察了三个恒星形成历史的示踪物（i波段绝对星等 M_i、[g-r]颜色和Halpha发射线当量宽度）以及两个星系形态指标（表面亮度和径向集中度），涉及红移范围为0.015<z<0.068的52,569个星系。 我们发现，我们的形态指标通过与恒星群体和恒星形成率的关系间接地与星团中心距离相关。 靠近星团中心的星系比位于或超出星团引力半径附近的星系更亮、更红且具有更低的Halpha EW（即更低的恒星形成率）。 这些星系属性与星团中心距离之间的详细关系取决于星团的丰富度。 对于更丰富的星团，我们发现：(i) 颜色和Halpha EW从星团中心到场值的变化更加突然，并且更接近星团引力半径发生；(ii) 颜色和Halpha EW的分布总体上比较少丰富星团的更窄。 我们还发现，亮度分布中的径向梯度在较小的星团周围最强，并随着星团丰富度的增加而减弱。 我们在大约一个引力半径（流入区）处发现了一个“特征距离”，在那里星系属性分布随半径的变化最为显著，但我们没有发现因流入触发的恒星爆发的证据。 这些结果表明，星系“知道”它们最近的星团的距离和大小，并在它们的恒星形成历史中表达这一信息。 显示英文摘要

摘要： We investigate the extent to which galaxies' star-formation histories and morphologies are determined by their clustocentric distance and their nearest cluster's richness. We look at three tracers of star-formation history (i-band absolute magnitude M_i, [g-r] color, and Halpha emission line equivalent width) and two indicators of galaxy morphology (surface brightness and radial concentration) for 52,569 galaxies in the redshift range of 0.015<z<0.068. We find that our morphology indicators relate to the clustocentric distance only indirectly through their relationships with stellar population and starformation rate. Galaxies that are near the cluster center tend to be more luminous, redder and have lower Halpha EW (ie, lower star-formation rates) than those that lie near or outside the virial radius of the cluster. The detailed relationships between these galaxy properties and clustocentric distance depend on cluster richness. For richer clusters, we find that (i) the transition in color and Halpha EW from cluster center to field values is more abrupt and occurs closer to the cluster virial radius, and (ii) the color and Halpha EW distributions are overall narrower than in less rich clusters. We also find that the radial gradient seen in the luminosity distribution is strongest around the smaller clusters and decreases as cluster richness increases. We find there is a `characteristic distance' at around one virial radius (the infall region) where the change with radius of galaxy property distributions is most dramatic, but we find no evidence for infall-triggered star bursts. These results suggest that galaxies `know' the distance to, and the size of, their nearest cluster and they express this information in their star-formation histories.